1. Field of the Invention
This invention relates generally to electronic copiers, fascimile transmission equipment, or similar apparatus having the capability of determining the size and location of an original document on a scanner platen.
2. Description of the Prior Art
Scanning apparatus frequently includes document recognition schemes to determine the size and position of an original document on the scanner platen so as to provide for such features as image shift, magnification (reduction and/or enlargement), automatic recording sheet selection, edge erase, book copying, and so forth. However, on typical scanners, intrack scanning can be performed in only one direction, and the scanner must go through two complete scan cycles for each document; first performing document recognition and then image capture. Each complete scan cycle requires the scanner to move across the platen first in a forward direction and then in a reverse direction to return to its "home" position. Thus, for two complete scan cycles, the time required to produce the first copy is doubled, and the throughput rate of the scanner is reduced.
There are some scanners which overcome the throughput rate problem by performing the document recognition and image capture functions simultaneously in a single pass of the scanner over the document. For example, see U.S. Pat. No. 4,554,592, which issued on Nov. 19, 1987 to T. Yoshida. While this greatly increases the scanner's throughput rate, it eliminates any possibility of automatic magnification to fit the image to a predetermined image area if the magnification is effected by adjusting either the rate that the image is scanned or the rate at which data is stored into a buffer memory. That is, intrack magnification done to fit the image onto a recording sheet of known size by adjusting the speed of the scanner drive requires the knowledge of the size of the original document before the document is scanned in order to compute the speed of the scan (intrack magnification) and the frequency that will be used for writing data to the buffer (crosstrack magnification). Effecting document recognition and image capture during the same pass of the scanner over the document does not provide the advance knowledge of the document size required for automatic magnification.